ABSTRACT: The common circum-tropical jellyfish Cassiopea sp., unlike other members of the Rhizostomidae (Scyphozoa), exhibits a primarily benthic life. The peculiar orientation of its exumbrella against the sediment is believed to be associated with its mainly autotrophic nutrition, i.e. exposing its zooxanthellae-bearing photosynthetic oral appendages to the sunlight. Here we show that the jellyfish also acts as a nutrient pump, drawing nutrient-rich pore waters from the permeable sediments. Depletion of pore-water ammonium in situ, light-enhanced ammonium uptake, and high rates of photosynthesis determined via oxygen flux measurements and underwater fluorometer analysis (rapid light curves) show that Cassiopea sp. effectively harnesses pore-water nutrients. At high densities Cassiopea sp. may facilitate benthic-pelagic coupling and primary production in oligotrophic coral reefs.